I. Field of the Invention
This invention relates generally to the field of geophysical prospecting and more particularly to improved means for coupling the energy of a seismic source into the earth in a manner to generate combined compressional and shear seismic waves.
II. Prior Art
Prior art devices for generation of combined compressional and shear seismic waves in the earth typically employ some means for applying a downwardly directed force in a direction inclined to the vertical against a ground coupling member so that the resultant downward movement of such member in the direction of the applied force produces the requisite seismic waves. One example of this type of prior art device is illustrated in U.S. Pat. No. 4,059,820 to Turpening.
A disadvantage inherent in such prior art devices is the failure of the ground coupling to provide for adequate penetration into the earth under a variety of soil conditions to insure maximum efficiency of earth coupling for generation of shear seismic waves. In addition, the prior art has not focused specifically on the need for maintaining exact correspondence between the direction of the applied force and the direction of penetration of the ground contacting means regardless of the orientation of the force generation device.
The applicant's invention is therefore directed to the redesign of a ground coupling device for a seismic source to overcome the disadvantages referenced above.